Half of US population could be harmed by earthquakes, see where Washington ranks

Half the United States population is at risk of being harmed by earthquakes, and tens of millions are in the bull’s-eye of much stronger earthquakes.

That’s the grim outlook of a U.S. Geological Survey report published earlier this month that focused on answering the great and terrible question: How devastating can earthquakes actually be to Americans and what should we do about it?

More than 143 million Americans living in the 48 contiguous states are exposed to potentially damaging ground shaking from earthquakes. When the people living in the earthquake-prone areas of Alaska, Hawaii and U.S. territories are added, this number rises to nearly half of all Americans.

And the punchline is?

“This new research helps us better understand the scale of earthquake hazards and ultimately strengthen the nation’s ability to protect Americans against future events,” said Kishor Jaiswal, a USGS research structural engineer as well as the lead author of the study. “Of particular concern is the significant amount of critical infrastructure located in high earthquake-hazard areas, ranging from private and public schools to health care facilities and fire stations. The USGS is dedicated to continuously updating research on population and infrastructure exposure as communities change and new science is available on earthquake behavior.”

This in the shadow of the attack on our peace of mind by the New Yorker that blew up the Internet. What we said, “The New Yorker takes a deep-dive into the coming megathrust earthquake along the Cascadia Subduction Zone that’s guaranteed to smash the hell out of everything west of the Cascades.”

Tsunamis!

So, earthquakes also lead to tsunamis, and just in case we’re not freaked out enough by the shaking, the University of Washington has sent out a Q and A with researchers who model tsunamis that would be generated by the great and terrible “mega-thrust Cascadia killer quake” due in the next couple of hundred years.

Video by Jake Ellison

Raw: NOAA tsunami propagation off NW coast

Here are two versions of how a tsunami caused by a mega-thrust earthquake in the NW Cascadia Subduction Zone would propagate. The models are from the NOAA Center for Tsunami Research.

How would a tsunami from a large offshore earthquake affect Puget Sound?

LeVeque: The tsunami would be coming from the open ocean, so it would come in through the Strait of Juan de Fuca and come down to Puget Sound. We’re just starting to look down there. But by the time the tsunami gets down into Puget Sound it will be smaller than on the coast.

Gonzalez: But in the case of a big magnitude-9 offshore earthquake, that will create shaking severe enough in Puget Sound to trigger small to moderate landslides, and they’ll create tsunamis as well.

So, is the tsunami danger in Puget Sound not as bad as the open coast?

LeVeque: Not nearly as much danger during an earthquake along the Cascadia subduction zone. But there’s also the Seattle Fault, which runs right across the Sound, and others like the Tacoma Fault and the South Whidbey Island Fault. These faults are actually under Puget Sound and can have big earthquakes and cause tsunamis.

Gonzalez: That Seattle Fault tsunami has been modeled by others. That wave is quite severe, quite high. And the magnitude used to generate that wave is only about 7.5, as opposed to a magnitude-9 earthquake off the coast. And since those models for the Seattle Fault were published, there’ve actually been many more Puget Sound faults discovered.

How useful can your models be for communities in tsunami hazard areas?

Gonzalez: People take the kind of information Randy and I provide about tsunami hazard and assess the vulnerability of communities, and emergency management officials assess preparedness efforts.

LeVeque: In Westport they just had their groundbreaking in January to build a new vertical evacuation structure for tsunamis at Ocosta Elementary. It happens to sit on a relatively high part of that peninsula. From the modeling that we did, it looks like under a worst-case scenario that the area right around the school would have only a couple of feet inundation.

Video by Jake Ellison

Tsunami Scenarios for Washington cities

These models were created by NOAA based on earthquakes in the Cascadia Subduction Zone, Seattle Fault and Tacoma Fault